Objective: The objective is to assess coronary endothelial function 6 months after zotarolimus-eluting stents(ZES) implantation compared with sirolimus-eluting stents(SES) implantation. Methods: Patients who had one stent implantation for single de novo lesion in left anterior descending artery were enrolled to this prospective study and classified to two groups by randomization of stent type: ZES and SES group. We performed 6 month-follow up angiography and assessed endothelial function in only patients who showed no angina during follow up period and no angiographic in-stent restenosis. Endothelium-dependent vasomotion was determined by measuring the change of diameter after selective intracoronary injection of acetylcholine(Ach, 10-6 mol/L). Endothelium-independent vasomotion was assessed after intracoronary bolus of 2mg-nitrates. The measuring was done at 5 segments; near proximal and proximal, distal and far distal, and stented segment by quantitative coronary angiography. Intravascular ultrasound was done to exclude patients who showed dissection or atherosclerosis in measuring points. Results: The assessment was performed in total 18 patients(7 of ZES, 11 of SES). In stented segments, no significant vasomotion was observed in both groups. In distal and far distal segments, SES group showed significant vasoconstriction by Ach. However, no significant vasomotion was observed in ZES group (SES vs ZES: -36.3% vs 2.7% for distal;p=0.002, -34.5% vs 1.2% for far distal;p=0.001). Comparing change of diameter between near proximal and far distal segments and between proximal and distal segments after Ach injection, ZES group showed no difference (p=0.77,0.48) while SES group showed significant decrease of diameter in distal portion compared to proximal portion (p=0.001,0.001). There was no difference in vasodilatation by nitrates between two groups. Conclusions: The impairment of endothelium-dependent vasodilatation in long distal portion was observed in SES group but not in ZES group. Endothelium-independent vasodilatation was intact in both groups. The results suggest that coronary endothelial function after ZES implantation could be recovered earlier than after SES implantation.